Helical device for cooling or heating

ABSTRACT

The efficiency of a device for cooling or heating objects on a belt that moves through a path of a helix, in which gaseous cooling or heating medium is circulated within the device, is improved by positioning fans that circulate the cooling or heating medium so that the fans are distanced from the top of the helix.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 62/683,301, filed on Jun. 11, 2018, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to devices useful for effecting rapid heattransfer to or from objects, such as the cooling and/or freezing or theheating and/or cooking of food or other products.

BACKGROUND OF THE INVENTION

Many industries, not least among them the food industry, find itnecessary in the course of their operations to be able to cool or heatproducts relatively rapidly.

When a product needing chilling or freezing is at room temperature, oris at temperatures higher than room temperature as the result of aprevious processing or cooking step, reducing the temperature of theproduct rapidly is desirable in order to minimize the ability ofunwanted physical or chemical changes to occur. When the product isfood, it is highly desirable to avoid enabling pathological organismssuch as bacteria to grow on or in a product, and (particularly when theproduct is to be frozen), to put the product into condition to bepackaged prior to its being stored and/or shipped to distributors orcustomers. Examples of products which benefit from this treatment, whichare also products that can be treated by the present invention, includeraw foods such as eggs, hamburger patties, fruits and vegetables, raw orcooked cuts of meat such as beef, pork, veal, lamb, poultry carcassesand poultry sections, as well as processed foods prepared by combiningvarious ingredients, such as pastries, pre-packaged entrees and completedinners.

When a product is to be heated or cooked, the ability to achieve thenecessary heat transfer rapidly is useful in order to minimize theopportunity for pathogens to grow, and to achieve a greater rate ofprocessing in a given period of time.

Many techniques are known for cooling and freezing large numbers ofproducts such as food products. Examples include impingement coolers,mechanical refrigerators, and other devices wherein the product isconveyed through a chamber wherein the product is exposed to lowtemperatures for a sufficient period of time to reduce the temperatureof the product to the desired final, cooled temperature.

Many techniques are also known for heating and cooking large numbers ofproducts such as food products, such as tunnel ovens and the like. Onepreferred type of device applicable to cooling/freezing andheating/cooking applications is known as a spiral or helical cooler orcooker, wherein at least a portion of the path that the product followsas it is conveyed through a chamber is in the form of a helix. Forexample, the product is placed on a moving flexible belt that follows apath which curves around on itself as it steadily climbs. With this typeof device, the product travels a longer distance and experiences alonger dwell time in the cooling or heating environment for a givenamount of area occupied by the device, taking advantage of the verticalarray of the belt.

Helical (also referred to as spiral) devices have heretofore presented adrawback that the successive tiers of the belt interfere with heattransfer from or to the product, because of the proximity of adjacenttiers which interfere with flow of cooling or heating air. Also, it haspreviously been considered necessary to include baffles and similarstructure to guide the flow of the gaseous heat transfer medium withinthe unit, but the resulting tortuous path leads to loss of efficiencyand loss of cooling capacity. The present invention provides devices andmethods that retain the advantages of helical devices but which achievefaster heat transfer to or from the product than has been available upto now.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present invention is a device useful for cooling orheating objects such as food products that pass through the device,comprising

a housing having a bottom, top, and side walls, which create an enclosedspace, and including first and second openings each of which is presentthrough a side wall between the enclosed space and the exterior of thehousing,

an endless movable belt that extends between the first and secondopenings and that follows within the housing a path a portion of whichis in the form of a helix which is oriented vertically around a verticalcentral space within the housing and includes a plurality of tiers ofthe belt that are arrayed vertically,outlets within the housing that are capable of dispensing heat transfermedium into the interior of the housing,a fan that is positioned in the vertical central space and that hasblades oriented so as to be capable of impelling gaseous heat transfermedium vertically through the blades and capable of impelling movementof gaseous heat transfer medium across the tiers in the housing,

-   -   wherein the fan is attached by a drive shaft to a motor that is        capable of rotating the shaft and the fan, and wherein the fan        is positioned in the vertical central space at a height such        that at least one tier, and preferably a plurality of tiers, of        the belt in the helix are located below the fan and at least one        tier, and preferably a plurality of tiers, of the belt in the        helix are located above the fan;        wherein there is circulation space within the housing between        all of the exterior edges of the belt in the helix and the        interior surfaces of the side walls, and between the topmost        tier of the belt and the interior surface of the top wall, and        there are openings between the vertical central space and the        interior edges of the belt in the helix, so that gaseous heat        transfer medium can be impelled by the fan across the upper        surfaces of the tiers of the belt in the helix between the        central space and the circulation space.

In alternate embodiments, there can be more than one such fan on theshaft.

In another aspect of the present invention, there is no structurepresent that would prevent flow of gaseous heat transfer medium betweenthe central space and the upper surfaces of any tiers of the belt in thehelix. In yet another aspect of the present invention, there is nostructure present between the topmost tier of the belt in the housingand the top wall of the housing.

Another aspect of the present invention is a method for cooling orheating objects such as food products, comprising

(A) providing a housing having (1) a bottom, top, and side walls, whichcreate an enclosed space, and including first and second openings eachof which is present through a side wall between the enclosed space andthe exterior of the housing, (2) an endless movable belt that extendsbetween the first and second openings and that follows within thehousing a path a portion of which is in the form of a helix which isoriented vertically around a vertical central space within the housingand includes a plurality of tiers of the belt that are arrayedvertically, (3) outlets within the housing that are capable ofdispensing heat transfer medium into the interior of the housing, and(4) circulation space within the housing between all of the exterioredges of the belt in the helix and the interior surfaces of the sidewalls, and between the topmost tier of the belt and the interior surfaceof the top wall, and there are openings between the vertical centralspace and the interior edges of the belt in the helix;(B) operating a fan that is positioned in the vertical central space ata height such that at least one tier, and preferably a plurality oftiers, of the belt in the helix are located below the fan and at leastone tier, and preferably a plurality of tiers, of the belt in the helixare located above the fan, and that has blades oriented so as to becapable of impelling gaseous heat transfer medium vertically through theblades and capable of impelling movement of gaseous transfer mediumacross the tiers in the housing, to cause gaseous heat transfer mediumto flow from the circulation space to the central opening betweenadjacent tiers of the belt in the helix that are on one side of the fan,and to cause gaseous heat transfer medium to flow from the centralopening to the circulation space between adjacent tiers of the belt inthe helix that are on the other side of the fan; and(C) moving the belt through the housing with objects on the belt whiledispensing heat transfer medium into the interior of the housing thatchills or heats the objects.

Preferred objects include food products, by which is meant edibleproducts, whether packaged or not packaged. Other objects with which theinvention may be useful include finished articles, raw metals and ores,powders, and medical products.

In a preferred embodiment of this method, gaseous heat transfer mediumflows through all of the spaces between the central opening and thecirculation space.

As used herein, “cooling” and its conjugate forms means removing heatfrom an article, and thus encompasses reducing the temperature of thearticle, freezing the article, or both reducing the temperature andfreezing.

As used herein, “heating” and its conjugate forms means adding heat toan article, and thus encompasses increasing the temperature of thearticle, cooking the article, or both increasing the temperature andcooking.

As used herein, “vertical” means not only exactly perpendicular to theearth's surface but also within an angle of up to 30 degrees, preferablyup to 10 degrees, relative to a line that is exactly perpendicular tothe earth's surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view in partial cutaway of a device with whichthe present invention is useful.

FIG. 2 is a cross-sectional view of an embodiment of the device of FIG.1.

FIG. 3 is a cross-sectional view of the embodiment of the invention ofFIG. 1 taken on line 3-3′ of FIG. 1.

FIG. 4 is a cross-sectional view of another embodiment of the invention.

FIGS. 5A and 5B are cross-sectional views of embodiments of theinvention employing two fans.

FIG. 6 is an expanded view of part of the embodiment of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the type of device with which the present invention isuseful appears in the drawing figures. However, these illustrations areprovided for purposes of description and are not intended to limit thedefinition of this invention.

The device generally comprises unit 10 comprising an insulated housing12, and an endless movable belt 24 that carries products 34 throughhousing 12. The device also comprises structure and components, notshown in FIG. 1, for cooling or heating the products as they passthrough the housing 12.

Housing 12 can take the form of a rectangular parallelepiped havingvertical walls 14, a top wall 16, and a bottom wall 18, all of which arepreferably sealed together and thermally insulated against heat flowtherethrough into or out of the interior of housing 12. One or moredoors 20, and optional window 22, can be provided to permit physical andvisual access to the interior. Control panel 21, containing controlssuch as for the operation of the belt, fan, and any cooling or heatingunit associated with the device, and conveniently also containing gaugesfor monitoring the conditions of the unit, can also be provided on theexterior of a wall 14.

The products to be cooled or heated are preferably conveyed on endlessbelt 24 which can be of known construction. The belt is preferablyporous enough to permit air to flow through it. Examples include beltsof unitary material such as a polymeric web of material, and belts ofinterlocked links of polymeric or metallic material which can flex andchange their position relative to adjacent links so as to accommodatethe belt being able to pass through the straight and curved portions ofthe belt's route. Material that serves as gaseous heat transfer mediumdescribed herein (such as chilled air, or cryogenic vapor) passesthrough open spaces between the links of this type of belt.

Loading (or unloading) station 26 is preferably provided adjacent to afirst opening 28 through one wall 14, and an unloading (or loading)station 30 outside a second opening 32 through the same or another wall14 is also provided. With these stations and openings, product can befed into and recovered from the unit 10 without the operator needing toenter the unit. The belt 24 extends between first opening 28 and secondopening 30, by which is meant that a product can be placed onto belt 24at one of said openings and removed from belt 24 at the other of saidopenings, from outside unit 10. The many ways that products can beplaced onto belt 24 include placing product onto belt 24 by hand, or bypositioning another conveyor outside the unit so that products can moveoff the end of the conveyor onto belt 24. Similarly, products can beremoved from belt 24 by hand, or by being moved off of belt 24 ontoanother conveyor outside the unit. Thus, the belt 24 can extend from theinterior of the housing 12 through openings 28 and 32 to outside thehousing, as shown in FIG. 1, but does not need to.

As shown in FIG. 1, one of the openings 28 and 32 is located at arelatively low elevation, such as at about the same level as the lowerend of the helix formed by the belt, and the other of these openings isat a relatively high level at the upper end of the helix. Product canpass from low to high, as indicated by the arrows in FIG. 1, or fromhigh to low. A small number of products 34 are shown in FIG. 1, forpurposes of illustration, but in actual practice the belt could becarrying a much higher number of products.

The belt 24 is driven through its path in any manner by suitableequipment. A preferred type of equipment employs a cylindrical cage 49which typically comprises a plurality of vertical bars 50 which arespaced apart from each so that gaseous heat transfer medium can flowbetween the bars. The bars 50 are arrayed in the form of a cylinder andare attached to circular rolled angles at the top (shown as 52) and thebottom (shown as 53)) and located around the outermost circumference ofcentral space 104 (see also FIG. 2) within the helix formed by thehelical portion of the belt. The outer surfaces of the bars 50 of cage49 frictionally engage the interior edges 24A of the belt 24 in thehelix. The cage 49 is rotated about its longitudinal (vertical) axis viaa motor 54 which is connected by suitable linkage to the cage, and therotation of the cage frictionally engages the belt and causes the beltto move through its path. A fuller description of this type of equipmentappears in U.S. Pat. No. 4,953,365.

The belt 24 can alternatively be moved through its path by any othersuitable equipment, such as the combination of a roller or pulley overwhich the belt passes and that engages the belt (such as by friction orby engagement of teeth on the roller with the belt material), and amotor and suitable connecting linkage by which the motor turns theroller or pulley and thereby causes the belt to move.

The path of belt 24 as shown in FIG. 1 extends within the housing 12between first opening 28 and then upward about a generally helical paththereby defining a plurality of tiers 38 and defining spaces 46 betweeneach pair of adjacent tiers 38. The tiers 38 are supported by aplurality of horizontal arms 40 which extend inward transversely andpreferably radially inward from posts 42 that extend between top wall 16and bottom wall 18. Circumferential support beams (some of which areshown as 51 and 53) are attached to the inner and outer ends,respectively, of the arms 40, and have curvature corresponding to thatof the inner and outer edges of the belt 24 so that the inner and outeredges of the belt are supported by and slide on the upper surfaces ofsupport beams 51 and 53. Other arrangements for structure that supportsthe belt and permits it to move are also known and can be employed, solong as they support the belt in the desired path and permit it to movealong the path (such as with the aid of rollers or roller bars on thearms 40). A suitable tensioning mechanism can be provided, such as isshown at 41, to help the belt to be sufficiently taut regardless ofchanges in its length caused by temperature differentials.

Referring also to FIG. 2, the housing 12 is dimensioned to providelateral circulation spaces 106 between the exterior edges 24B of thebelt 24 in the helix and the interior surfaces of walls 14. The housingis furthermore dimensioned to provide top circulation space 107 betweenthe topmost tier of the belt and the interior surface of top wall 16.

The gaseous heat transfer medium is often air. For cooling purposes, theinvention can be practiced using chilled air, or injected cryogen suchas liquid nitrogen or liquid carbon dioxide, as discussed below. Forheating purposes, air can be used as the heat transfer medium, as canother heat-carrying substances such as steam. The present invention willbe described first with reference to cooling using air.

There are several ways that can be employed to cool air for use in thepractice of the present invention. In the embodiment of the inventionshown in FIG. 2, the air within housing 12 is cooled by cooler 110.Cooler 110 comprises any conventional heat exchange device by whichcooling fluid 112, such as air, passes through cooler 110 and is fedfrom outlets 114 into housing 12 after having been chilled in cooler 110via indirect heat exchange by coming into contact with piping or othersurfaces which are colder than the fluid entering into cooler 110. Onepreferred technique is to contact the air with piping that containsmixed carbon dioxide-ammonia refrigerant, which is generally at minus 62degrees F. to minus 63 degrees F., so that the air is chilled to aboutminus 52 degrees F. to minus 53 degrees F. Another preferred techniqueis to use as the refrigerant a multicomponent refrigerant such asdisclosed in U.S. Pat. No. 6,176,102, which permits the cooling surfacesto have a temperature even as low as about minus 140 degrees F. so thatthe air can be chilled to about minus 125 degrees F.

Another technique to provide cooling to product in the device of thisinvention is to use liquid cryogen such as liquid nitrogen or liquidcarbon dioxide, which are of course very cold before and after theyevaporate. Referring to FIGS. 3 through 6, liquid cryogen is fed underpressure into the interior of housing 12 via line 192 and is sprayedonto products on belt 24. Vaporization of the injected cryogen withdrawsheat and provides a very cold gaseous heat transfer medium. Thus, whencryogen vapor is employed as the cooling medium, cooler 110 is notneeded.

Referring to FIGS. 3, 4, 5A and 5B, (in which, for purposes of clarity,not all features of the invention may be shown in every Figure) in onepreferred mode of spraying the cryogen one or more of the arms 40 arehollow and have on the underside a plurality of nozzles 302 whichdischarge toward the belt 24. Line 192 from outside housing 12 isconnected to opening 304 in the end of each arm 40 that is soconstructed, and cryogen fed into opening 304 emerges under pressurefrom nozzles 302 toward and onto the belt and onto product 34 that is onthe belt. Line 192 is connected outside housing 12 to a tank or othersuitable source of cryogen under pressure.

If the operator observes that the rate of heat transfer (or the extentof chilling or freezing) to a belt surface is higher nearer to aninterior edge 24A and less nearer to an exterior edge 24B, then theflows of heat transfer medium out of nozzles 302 can be varied so thatthe flow from the nozzles nearer to edge 24A is less than the flow fromthe nozzles nearer to edge 24B. Flows can be varied by using nozzleswith different sized openings.

In embodiments in which products on the belt are to be heated, theembodiment in FIG. 2 can be employed in which cooler 110 is replaced byan air heater which is a source of heated air that serves as the heattransfer medium which is circulated and impinged upon the product.Alternatively, the arrangement in FIGS. 3 through 6 can be employed inwhich line 192 feeds steam from a source such as a steam generator, oranother high-temperature fluid from a suitable source thereof, throughopening 304 into arms 40 and out nozzles 302. The thus ejected steam orother fluid performs as a hot heat transfer medium.

In any of the embodiments of the present invention, an impeller 100 ispresent to provide convective heating or cooling. Impeller 102 ispositioned in central space 104 and includes shaft 101 which is attachedto motor 44 that, when operating, rotates shaft 101. While motor 44 isshown in the Figures as located on top wall 16, the motor 44 thatrotates shaft 101 can be situated elsewhere in the unit and connectedvia suitable linkages so that operation of the motor 44 causes shaft 101to rotate. Shaft 101 can extend downward from top wall 16, which is alsoits preferred point of attachment to motor 44 as shown in FIGS. 2, 3, 4,5A and 5B. As can be seen in FIGS. 2, 3, 5A and 5B, shaft 101 can extenddownward from top wall 16 part of the distance toward bottom wall 18, sothat the lower end of shaft 101 is between top wall 16 and bottom wall18. However, if desired, as can be seen in FIG. 4, shaft 101 can extendall the way from top wall 16 to bottom wall 18. In either embodiment, itis preferred to provide one or more bearings 101A which are secured to awall of the housing 12, such as top wall 16 and/or bottom wall 18,and/or to structure that is in turn attached to top wall 16 or bottomwall 18 (such as arm 101B that appears in FIG. 3). Any such bearingsshould permit the shaft to rotate freely within each bearing, and wouldhold the shaft 101 in its axial position to restrain it from deviatingfrom its desired axial position while it rotates.

One or more fans 102 are attached to shaft 101. Each fan 102 containsone or more blades 103. The fans 102 and blades 103 are fixed inposition so that rotation of shaft 101 causes each fan and its blades torotate about the axis of shaft 101. The blades of each fan 102 (or ofone fan 102 when only one fan is present) should be angled to drivegaseous atmosphere in a vertical direction from the blades, which isupwards or downwards depending on the direction of rotation of shaft101.

The diameter of the blades 103 inside the central space 104 must ofcourse provide a large enough gap to safely be rotated without the tipsof the blades hitting the interior belt edges 24A or the inside surfacesof the cage bars for all conditions and bearing locations. The gapbetween the tip of each blade 103 and the belt edges 24A, or the cagebars, whichever is closer to shaft 101, is typically 1 inch or more.This allows for safe operation of the impeller 100 during operation,even when ice may have built up on the blades 103 which could change theeffective length of a blade 103 or could cause vibration because of theextra weight that would be caused by the ice. Shorter blade diameters,even presenting a gap of up to about 6 inches between the blade tip andthe vertical bars of the cage, have been tested successfully running athigher rotational speed to provide the same volumetric flow rate ofatmosphere through space 104.

Each fan 102 is positioned in central space 104 between the topmost andbottommost tiers 38 of the belt 24 in the helix. When there is one fan102 present, one tier 38 (as shown in FIG. 2) or a plurality of tiers 38(one example of which is shown in FIG. 4) of the belt 24 are above theplane of fan 102, and one tier 38 or a plurality of tiers 38 are belowthe plane of fan 102. By “plane of the fan” is meant the horizontalplane, perpendicular to shaft 101, in which the radial axes of theblades 103 lie. In embodiments wherein more than one fan is present,such as the embodiments of FIGS. 5A and 5B in which fans 102A and 102Bare present, one tier 38 or a plurality of tiers 38 of the belt 24 areabove the plane of the fan that is closest to the top wall 16, and onetier 38 or a plurality of tiers 38 of belt 24 are below the plane of thefan that is closest to the bottom wall 18, and there should also be aplurality of tiers 38 between the planes of the two fans. More than twofans may be provided on shaft 101, up to four or five, but one or twofans are adequate to provide the improved flow and the improvedefficiency that are realized with this invention. Alternatively, asshown in FIG. 5B, fan 102A is attached to shaft 101 which is driven bymotor 44, whereas fan 102B is attached to another shaft 101B which isdriven by motor 44B.

Rotation of the fan or fans causes gaseous atmosphere on one side ofeach of the one or more fans 102 to be drawn across belt surfaces 24 oneach tier from the circulation space 106 into the central space 104,while causing gaseous atmosphere on the other side of the fan to beforced across belt surfaces on each tier from the central space 104 tothe circulation space 106. As the gaseous atmosphere is drawn or forcedacross each belt surface, the atmosphere contacts the objects (such asfood products) that are on each such belt surface and cools them (orheats them, depending on the intended function of the apparatus and onthe temperature of the heat transfer medium relative to the products34). It will be understood that whereas the gaseous atmosphere flows inan essentially vertical direction as it passes through the plane of theblades 103, the flow of the atmosphere toward the blades and away fromthe blades will be not just vertical but also out of the spaces 46between each tier 38 of the belt 24 in the helix on the upstream side ofthe fan, and into the spaces 46 between each tier 38 of the belt in thehelix on the downstream side of the fan. Of course, the blades are“pitched” by which is meant that the blades as attached to the fan liein a plane that is not horizontal and not vertical but is at an anglerelative to the horizontal plane containing the radius of the blade.

One flow pattern is illustrated by the large arrows in FIG. 2. In thisembodiment, the combination of the direction of rotation of shaft 101and the direction in which fan blades 103 are pitched causes the heattransfer medium to be drawn from circulation spaces 106 into and throughthe spaces 38 between the tiers of belt 24 that are above the plane offan 102 (thereby passing across the surfaces of belt 24 in those spacesand contacting product 34 that is on those surfaces) as well as throughtop circulation space 107, into space 104 above fan 102, then forceddownward through fan 102 and into and through the spaces 38 betweenacross the tiers of belt 24 that are below the plane of fan 102 (therebypassing across the surfaces of belt 24 in those spaces and contactingproduct 34 that is on those surfaces), and then into the circulationspaces 106.

It will be recognized that the direction of flow shown in FIG. 2 can bereversed, if the direction of rotation of shaft 101 is reversed or ifthe blades 103 are pitched in the other direction. Then, the heattransfer medium would be drawn from circulation spaces 106 into andthrough the spaces 38 between the tiers of belt 24 that are below theplane of fan 102 (thereby passing across the surfaces of belt 24 inthose spaces and contacting product 34 that is on those surfaces), intospace 104, then forced upward through fan 102 and into and through thespaces 38 across the tiers of belt 24 that are above the plane of fan102 (thereby passing across the surfaces of belt 24 in those spaces andcontacting product 34 that is on those surfaces), as well as through topcirculation space 107, and then into the circulation spaces 106.

The positioning of the fan 102 (or multiple fans) can advantageously beestablished by reference to the Vertical Stack Length, which is definedas the vertical distance between the point at which the belt enters thehousing and the vertical distance between the point at which the beltexits the housing. The bottom position of the fan blades 103 should be adistance that is at minimum about 10% of the Vertical Stack Length belowthe level at which the belt exits and that is at maximum about 50% ofthe of the Vertical Stack Length below the top of the belt stack.Optimally this fan position should be a distance of between 20% and 40%of the Vertical Stack Length below the level at which the belt exits thehousing. At distances below the level at which the belt exits thehousing of less than 20% of the Vertical Stack Length, the fan is soclose to the top of the apparatus that there can be high velocities andhigh pressure drops on the inlet that lower the performance and flowrate of the fan, which can reduce the heat transfer and freezing orheating capacity of the apparatus. At distances below the level at whichthe belt exits the housing of more than 50% of the Vertical StackLength, the shaft that is driving the fan can become long enough that itcan become difficult to stabilize at the high rotational speeds that arerequired to produce high velocities and flow rates across the tiers.

The positioning of the fan as described herein enables the user tooperate without any baffles or other structure, above the topmost tierof the belt other than the top wall itself, that would completely blockflow of gaseous heat transfer medium between the topmost tier of thebelt and the top wall of the housing. The positioning of the fan asdescribed herein also enables the user to operate without any baffles orother structure that would prevent the gaseous atmosphere from passingin either direction into or out of the space between tiers of the helix,between circulation space 106 and central space 104. However, the usermay find it advantageous to include a modified baffle 120 in the regionof central space 104 that extends from the lowest tier of belt 24 as farupward as 10 to 15% of the distance from the lowest tier of belt 24 tothe inside surface of top wall 16 of the housing. Typically thismodified baffle 120 extends across the openings between space 104 andthe bottom 1 to 3 tiers of the helix. Such a baffle should be perforate,that is, not completely impermeable but having openings (holes or slots)through it to permit some gaseous atmosphere to pass through it. This isadvisable to reduce the velocity of the atmosphere across the lowesttiers of the belt in the helix when the product on the belt isrelatively light, while still permitting heat transfer medium to flowacross the tiers and contact products on those tiers.

In the embodiments of FIGS. 5A and 5B, the blades of the two fans 102Aand 102B are preferably pitched in opposing directions, although this isnot absolutely necessary. When the blades are pitched in opposingdirections, then rotation of shaft 101 in one direction will cause theheat transfer medium to be drawn from circulation spaces 106 into andthrough the spaces 38 between the tiers of belt 24 that are above theplane of the fan 102B that is positioned lower on shaft 101 and belowthe plane of fan 102A that is positioned higher on shaft 101 (therebypassing across the surfaces of belt 24 in those spaces and contactingproduct 34 that is on those surfaces), into the region of space 104 thatis between the fans, then forced upward through fan 102A and downwardthrough fan 102B, and into and through the spaces 38 across the tiers ofbelt 24 that are above the plane of fan 102A (thereby passing across thesurfaces of belt 24 in those spaces and contacting product 34 that is onthose surfaces), as well as through top circulation space 107, and intoand through the spaces 38 across the tiers of belt 24 that are below theplane of fan 102B (thereby passing across the surfaces of belt 24 inthose spaces and contacting product 34 that is on those surfaces), andthen into the circulation spaces 106.

If the shaft 101 is rotated in the opposite direction, then thedirections of these flows would be reversed. That is, the gaseous heattransfer medium would be drawn from circulation spaces 106 that areabove the plane of fan 102A and those that are below the plane of fan102B, across the tiers of belt 24 into space 104 above and below therespective fans, then through fans 102A and 102B into the region ofspace 104 that is between the planes of fans 102A and 102B, and thenacross the tiers that are between the planes of those fans, intocirculation spaces 106.

Where two fans 102A and 102B are present and their blades are pitched inthe same direction, the overall flow pattern will resemble that of FIG.2, in either of two overall patterns: with flow passing from spaces 106,across the tiers that are above the plane of the higher fan 102A andinto space 104 above the plane of fan 102A, then through fan 102A andacross the tiers that are below the plane of fan 102A and into spaces106; or with flow passing from spaces 106, across the tiers that arebelow the plane of the lower fan 102B and into space 104 below the planeof fan 102B, then through fan 102B and across the tiers that are abovethe plane of fan 102B and into spaces 106.

There are significant variations in the vapor velocities over theproduct in a radial flow helical device depending on the location withinthe enclosure. A series of measurements were made at different positionson the belt (inside edge to outside edge) and different tier heightswithin the helix. The airflow measurements in radial flow helicalfreezers with a fan only at the very top of the belt stack indicate thata global average velocity across all tiers of about 325 feet per minuteis achieved. When the fan is in a position according to the presentinvention and the top and bottom flow baffles are removed, the globalaverage velocity measured is raised to 829 feet per minute. Thisrepresents a factor of a 2.55 increase in the velocity of cooling orheating medium over the products on the belt, and produces a freezerwith much higher capacity for freezing or chilling.

Computational fluid dynamics (CFD) modeling of the helical freezergeometry with both the current radial airflow and the improved radialairflow also indicate a much higher average velocity is achieved withthe lower fan position. The lower velocities on the inlet of the fan aparticularly important to decreasing the pressure drop across the fanand increasing the flow through the fan.

The device of the present invention has numerous advantages relative toprevious designs. Compared to other radial flow freezers, the new vaporflow pattern is more efficient with a lower pressure drop that enableslower power to drive the fan, a higher fan capacity, and highervelocities. Higher average vapor velocity on the belt surface driveshigher levels of convection cooling. This increased rate of convectionenables a higher freezing (or cooking) capacity in lb/hr in the sameavailable space due to the better airflow. Other radial flow devicesinclude top baffles to direct the flow where it is needed, but no topbaffles are needed for the new flow design of the present invention.

Compared to freezers that employ horizontal flow of the cooling medium,the present invention provides higher average velocity for a lower powerinput. Also, the present invention does not require a solid center cageor additional baffles to force flow across the belt surface. All flow onboth the inlet and outlet side of the fan produces velocity across thebelt, so there is minimal wasted velocity that does not pass over theproduct.

Compared to freezers that employ vertical flow of the cooling medium,the present invention requires much lower power input to produce highgas velocities across the belt. The added expense and complexity ofclosing off the belt edges and cage to flow is not required with theimproved flow path of the present invention.

Other advantages of the present invention include higher capacity andsmaller equipment size. As the convection cooling is significantlyenhanced, a smaller lower cost freezer will be required for many users.The absence of any required flow-directing baffles opens up the freezerto both better airflow and easier sanitation of the equipment at the endof the production shift. Additional advantages of the present inventioninclude lower operating cost per pound of production; lower powerrequirements and higher capacity drive a lower cost of operation perunit of capacity. The advantages of the present invention are especiallypronounced for cryogenically cooled freezers.

The location of the fan according to the present invention is betweensections of the flow resistance. This allows the flow of gaseous heattransfer medium on the tiers above the fan position to be driven by thesuction into the fan and the flow on the tiers below the fan position tobe driven by the positive pressure output of the fan. As a result, thereis little or no wasted velocity produced.

Dividing the flow resistance into two sections (above and below the fan)lowers the flow resistance in each section and products highervelocities. The lower flow resistance results in lower pressure drop,which produces much higher gas flow rates and velocities across theproduct on the belt with the same power consumed in producing the flowof the gas.

The overall circuit length of the flows of the gaseous heat transfermedium is minimized which maximizes the velocity across the belt for agiven horsepower of used to create the gas flow. When the outlet of thefan pushes the flow at high velocities across the belt inside to outsidebelow the fan blade, the inlet of the fan pulls the flow at highvelocity from outside to inside across the belt positioned above the fanblade.

Also, the present invention employs a much larger effective inlet flowarea to the fan, that reduces pressure drop on the inlet to the fan.

The device of the present invention can be used to cool, freeze, or forma frozen crusted outer surface, on products that are at room temperatureor that are cooler or warmer than room temperature, especially includingproducts that have just been cooked or have just been cut from freshlyslaughtered animals. It can be used to warm or cook objects that enterat room temperature or at temperatures higher or lower than roomtemperature, especially including products that are fresh or have beenstored in chilled or frozen conditions.

The device of the present invention affords numerous advantages. Theprincipal advantage is a much higher rate of heat transfer from theproduct relative to the amount of cryogen employed. This advantage leadsto several other advantages: for a given size of device, more productcan be cooled or heated, and/or product can be cooled (or heated) to alower (or higher) temperature; a given amount of cooling or heating canbe achieved in a much shorter period of time; and a given amount ofproduct can be cooled or heated more quickly in a smaller unit thanheretofore needed.

In particular, when this invention is used to freeze at least the outersurface of a product, the product retains a greater proportion of itsinternal moisture compared to freezing using previously known devices,because other freezing regimens permit a greater amount of that moistureto be lost from the product before a frozen outer layer forms thatprevents further moisture loss. The more rapid cooling and freezing andthis invention provides establishes that frozen outer layer much morequickly, thereby retaining more of the internal moisture. This advantageis especially useful when the product being treated is warm and/ormoist, such as freshly produced raw-meat, freshly cooked meat, andfreshly steamed or cooked vegetables.

What is claimed is:
 1. A device for cooling or heating objects that passthrough the device, comprising a housing having a bottom, top, and sidewalls, which create an enclosed space, and including first and secondopenings each of which is present through a side wall between theenclosed space and the exterior of the housing, an endless movable beltthat extends between the first and second openings and that followswithin the housing a path a portion of which is in the form of a helixwhich is oriented vertically around a vertical central space within thehousing and includes a plurality of tiers of the belt that are arrayedvertically, outlets within the housing that are capable of dispensinggaseous heat transfer medium into the interior of the housing, one ormore than one fan that is positioned in the vertical central space andthat has blades oriented so as to be capable of impelling gaseous heattransfer medium vertically through the blades and capable of impellingmovement of gaseous heat transfer medium across the tiers in thehousing, wherein the one or more than one fan is attached by a driveshaft to a motor that is capable of rotating the shaft and the fan, andwherein the fan is positioned in the vertical central space at a heightsuch that at least one tier of the belt in the helix is located belowthe plane of the fan and at least one tier of the belt in the helix islocated above the plane of the fan; wherein there is circulation spacewithin the housing between all of the exterior edges of the belt in thehelix and the interior surfaces of the side walls, and between thetopmost tier of the belt and the interior surface of the top wall, andthere are openings between the vertical central space and the interioredges of the belt in the helix, so that rotation of the fan or fanscauses gaseous heat transfer medium on one side of the fan or fans to bedrawn across the upper surfaces of each tier of the belt in the helixfrom the circulation space into the central space, and causes gaseousheat transfer medium on the other side of the fan or fans to be forcedacross the upper surfaces of each tier of the belt in the helix from thecentral space into the circulation space.
 2. A device according to claim1 wherein there is one such fan that is positioned in the verticalcentral space.
 3. A device according to claim 1 wherein there is nostructure present above the fan that would impede flow of gaseous heattransfer medium between the central space and the top surfaces of thetiers of the belt in the helix.
 4. A device according to claim 1 whereinthere is no structure present that would prevent flow of gaseous heattransfer medium between the topmost tier of the belt in the housing andthe top wall of the housing.
 5. A device according to claim 2 whereinthere is no structure present above the fan that would impede flow ofgaseous heat transfer medium between the central space and the topsurfaces of the tiers of the belt in the helix.
 6. A device according toclaim 2 wherein there is no structure present that would prevent flow ofgaseous heat transfer medium between the topmost tier of the belt in thehousing and the top wall of the housing.
 7. A device for cooling orheating objects that pass through the device, comprising a housinghaving a bottom, top, and side walls, which create an enclosed space,and including first and second openings each of which is present througha side wall between the enclosed space and the exterior of the housing,an endless movable belt that extends between the first and secondopenings and that follows within the housing a path a portion of whichis in the form of a helix which is oriented vertically around a verticalcentral space within the housing and includes a plurality of tiers ofthe belt that are arrayed vertically, outlets within the housing thatare capable of dispensing gaseous heat transfer medium into the interiorof the housing, two fans that are positioned in the vertical centralspace and that have blades oriented so as to be capable of impellinggaseous heat transfer medium vertically through the blades and capableof impelling movement of gaseous heat transfer medium across the tiersin the housing, wherein the fans are attached one above the other to acommon drive shaft that is attached to a motor that is capable ofrotating the shaft and the fans, or to separate drive shafts eachattached to a motor that is capable of rotating the shaft and the fan,and wherein the fans are positioned in the vertical central space atheights such that at least one tier of the belt in the helix is locatedabove the plane of the higher fan, and at least one tier of the belt inthe helix is located below the plane of the lower fan, and a pluralityof tiers of the belt in the helix are located between the planes of thefans; wherein there is circulation space within the housing between allof the exterior edges of the belt in the helix and the interior surfacesof the side walls, and between the topmost tier of the belt and theinterior surface of the top wall, and there are openings between thevertical central space and the interior edges of the belt in the helix,so that rotation of the fans causes gaseous heat transfer medium on oneside of the fans to be drawn across the upper surfaces of each tier ofthe belt in the helix from the circulation space into the central space,and causes gaseous heat transfer medium on the other side of the fans tobe forced across the upper surfaces of each tier of the belt in thehelix from the central space into the circulation space.
 8. A deviceaccording to claim 7 wherein there is no structure present above the fanthat would impede flow of gaseous heat transfer medium between thecentral space and the top surfaces of the tiers of the belt in thehelix.
 9. A device according to claim 7 wherein there is no structurepresent that would prevent flow of gaseous heat transfer medium betweenthe topmost tier of the belt in the housing and the top wall of thehousing.